Proposal: Add concise syntax for separating namespace and module declarations

**I propose we** introduce a more concise syntax for separating namespace from file-level module name.

```F#
namespace Stroke and
module Characters
let content = ()
```

**The existing ways of approaching this problem in F# are**:
```fsharp
// Approach 1: Dotted module names
module Stroke.Characters
let content = ()

// Approach 2: Namespace + module
namespace Stroke
module Characters =
let content = ()
```

## Pros and Cons

**The advantages of making this adjustment to F# are**:
- Better refactoring support compared to dotted syntax (easier copy-paste and find-replace)
- Reduced indentation levels compared to traditional namespace + module approach
- Maintains clear namespace organization structure
- Provides improved code flexibility for large codebases
- More compact code layout while preserving readability

**The disadvantages of making this adjustment to F# are**:
- Introduces a new syntax variant, potentially increasing language complexity
- Developers need to learn the new syntax format
- Requires updates to compiler and toolchain support
- May conflict with existing coding style guidelines
- Could lead to inconsistency across codebases during transition period

## Extra information

**Estimated cost (XS, S, M, L, XL, XXL):** XS
(This is primarily a coding style recommendation rather than a language change)

**Related suggestions:** None identified

## Affidavit (please submit!)

Please tick these items by placing a cross in the box:
* [x] This is not a question (e.g. like one you might ask on [StackOverflow](http://stackoverflow.com)) and I have searched StackOverflow for discussions of this issue
* [x] This is a language change and not purely a tooling change (e.g. compiler bug, editor support, warning/error messages, new warning, non-breaking optimisation) belonging to [the compiler and tooling repository](https://github.com/dotnet/fsharp)
* [x] This is not something which has obviously "already been decided" in previous versions of F#. If you're questioning a fundamental design decision that has obviously already been taken (e.g. "Make F# untyped") then please don't submit it
* [ ] I have [searched both open and closed suggestions on this site](http://github.com/fsharp/fslang-suggestions/issues) and believe this is not a duplicate

Please tick all that apply:
* [x] This is not a breaking change to the F# language design
* [x] I or my company would be willing to help implement and/or test this

## For Readers

If you would like to see this issue implemented, please click the :+1: emoji on this issue. These counts are used to generally order the suggestions by engagement.

The proposal defines a new F# namespace-and-module declaration syntax and contrasts it with dotted names and traditional namespace-plus-module syntax. Begin by reviewing the compiler and toolchain areas that handle these declarations; done means the proposed form is accepted while existing approaches and language behavior remain supported.

Written by the indexing model from the issue text.